Both analog and digital image data transmission methods are known for transmitting image data. In order to guarantee high image resolution, transmission methods that guarantee reliable data transmission at a high data throughput are required. In particular, interfaces and transmission methods in which image data is transmitted in parallel through a plurality of lines are known for this purpose. In addition to the actual image data information that describes the individual pixels, control information that is used for line synchronization or frame synchronization, for example, is also be transmitted. For this purpose, it is known to transmit all control signals through one of the data lines. Furthermore, U.S. Pat. No. 5,859,669 discusses an interface and an image data transmission method in which this control information is co-transmitted through a clock signal line that is used to control image data transmission. In order to check whether data is transmitted correctly, it is also known to add to the transmitted data additional test data that is transmitted together with the actual data. However, this test data reduces the volume of user data that may be transmitted since the transmission frequency may not be increased at will. To be able nevertheless to transmit a maximum volume of data, the check of the transmitted data is omitted, as in U.S. Pat. No. 5,859,669, for example.